Microsoft recently published .Net Framework 4.6.1 as an inplace upgrade to the .Net Framework versions 4, 4.5, 4.5.1, 4.5.2 and 4.6. You can obtain the package via WSUS or Windows Update – but do not install it on an Exchange server.
As there can occur several issues in Exchange Server environments after installing .Net Framework 4.6.1 that version is not officially supported on Exchange Server in any version. Issues you can face are mailboxes that are quarantined without a reason or databases that unexpectedly fail over. You can find more information about these issues on Microsoft’s support site. An Exchange Server supportability matrix can be found in Technet Library.
You can block the installation via WSUS or Windows Update globally or for a dedicated server. You can also use client side registry settings to avoid the update to be installed.
If you face any of the issues above make sure that you have not installed .Net Framework 4.6.1 or to uninstall it again.
Update 2016/06/22: Two days ago, Microsoft published Exchange Server 2013 CU13 and Exchange Server 2016 CU2 and now .Net 4.6.1 is fully supported in these two Exchange versions. Make sure to install the following post release hotfix for .Net in your Windows Server version in order to be fully supported:
- Windows Server 2008/2008R2 – KB3146716
- Windows Server 2012 – KB3146714
- Windows Server 2012R2 – KB3146715
You can find further information on the Microsoft Exchange Team Blog.